Protein degradation is a highly regulated and essential process that maintains cellular homeostasis. The selective identification and removal of damaged, misfolded, or excess proteins is achieved via the ubiquitin-proteasome pathway (UPP). The UPP in fact is central to the regulation of almost all cellular processes, including antigen processing, apoptosis, biogenesis of organelles, cell cycling, DNA transcription and repair, differentiation and development, immune response and inflammation, neural and muscular degeneration, morphogenesis of neural networks, modulation of cell surface receptors, ion channels and the secretory pathway, the response to stress and extracellular modulators, ribosome biogenesis and viral infection.
Covalent attachment of multiple ubiquitin molecules by an E3 ubiquitin ligase to a terminal lysine residue marks the protein for proteasome degradation, where the protein is digested into small peptides and eventually into its constituent amino acids that serve as building blocks for new proteins. Defective proteasomal degradation has been linked to a variety of clinical disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, muscular dystrophies, cardiovascular disease, and cancer among others.
There are over 600 E3 ubiquitin ligases which facilitate the ubiquitination of different proteins in vivo, which can be divided into four families: HECT-domain E3s, U-box E3s, monomeric RING E3s and multi-subunit E3s. See generally Li et al. (PLOS One, 2008, 3, 1487) titled “Genome-wide and functional annotation of human E3 ubiquitin ligases identifies MULAN, a mitochondrial E3 that regulates the organelle's dynamics and signaling.”; Berndsen et al. (Nat. Struct. Mol. Biol., 2014, 21, 301-307) titled “New insights into ubiquitin E3 ligase mechanism”; Deshaies et al. (Ann. Rev. Biochem., 2009, 78, 399-434) titled “RING domain E3 ubiquitin ligases.”; Spratt et al. (Biochem. 2014, 458, 421-437) titled “RBR E3 ubiquitin ligases: new structures, new insights, new questions.”; and Wang et al. (Nat. Rev. Cancer., 2014, 14, 233-347) titled “Roles of F-box proteins in cancer.”.
In 1995, Gosink et al. (Proc. Natl. Acad. Sci. USA 1995, 92, 9117-9121) in a publication titled “Redirecting the Specificity of Ubiquitination by Modifying Ubiquitin-Conjugating Enzymes”, provided proof of concept in vitro that engineered peptides can selectively direct ubiquitination of intracellular proteins. The publication by Nawaz et al. (Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 1858-1862) titled “Proteasome-Dependent Degradation of the Human Estrogen Receptor” describes ER degradation which takes advantage of the ubiquitin-proteasome pathway.
Proteinex, Inc. filed a patent application in February 1999 that issued as U.S. Pat. No. 6,306,663 claiming a method of generating a compound for activating the ubiquitination of a Target Protein which comprises covalently linking a Target Protein binding element able to bind specifically to the Target Protein via a ubiquitination recognition element. Proteinex described that the invention can be used to control protein levels in eukaryotes. While the '663 patent may have been based on the first patent application to describe the high-level concept of how to manipulate the UPP system to degrade selected proteins in vivo, the patent did not provide sufficient detail to allow persons of skill to easily construct the range of proposed compounds. For example, for the ubiquitination recognition elements, the skilled person was told among other things to use standard methods for drug discovery and screen for appropriate small molecules that would bind to the ligase. Proteinex also emphasized the use of peptides as ubiquitination recognition elements, which can pose significant difficulties for oral drug administration.
Since then, harnessing the ubiquitin-proteasome pathway for therapeutic intervention has received significant interest from the scientific community. The publication by Zhou et al. from Harvard Medical School (Mol. Cell 2000, 6, 751-756) titled “Harnessing the Ubiquitination Machinery to Target the Degradation of Specific Cellular Proteins” described an engineered receptor capable of directing ubiquitination in mammalian and yeast cells.
Following from these early publications and others in the mid to late 1990s, it was also recognized by Craig Crews and coworkers (Yale University) that a molecule that is capable of binding a Target Protein and a ubiquitin ligase may cause the Target Protein to be degraded. Their first description of such compounds was provided in U.S. Pat. No. 7,041,298 filed in September 2000 by Deshaies et al. and granted in May 2006 titled “Proteolysis Targeting Chimeric Pharmaceutical”, which described a “PROTAC” consisting of a small molecule binder of MAP-AP-2 linked to a peptide capable of binding the F-box protein β-TRCP. Information in the '298 patent is also presented in the corresponding publication by Sakamoto et al. (Proc. Natl. Acad. Sci. USA 2001, 98, 8554-8559) titled “Protacs: Chimeric Molecules That Target Proteins to the Skp1-Cullin-F Box Complex for Ubiquitination and Degradation”. The publication by Sakamoto et al. (Mol. Cell. Proteomics 2003, 2, 1350-1358) titled “Development of Protacs to Target Cancer-Promoting Proteins for Ubiquitination and Degradation” describes an analogous PROTAC (PROTAC2) that instead of degrading MAP-AP-2 degrades estrogen and androgen receptors.
The first E3 ligase successfully targeted with a small molecule was MDM2, which ubiquitinates the tumor suppressor p53. The targeting ligand was an HDM2/MDM2 inhibitor identified in Vassilev et al. (Science 2004, 303, 844-848) titled “In Vivo Activation of the P53 Pathway by Small-Molecule Antagonists of MDM2”.
Other examples of direct small molecule-induced recruitment of Target Proteins to the proteasome for degradation on addition to cultured cells were described in 2004 (Schneekloth et al. (J. Am. Chem. Soc. 2004, 126, 3748-3754) titled “Chemical Genetic Control of Protein Levels: Selective in Vivo Targeted Degradation”). Schneekloth et al. describe a degradation agent (PROTAC3) that targets the FK506 binding protein (FKBP12) and shows that both PROTAC2 and PROTAC3 hit their respective targets with green fluorescent protein (GFP) imaging. The publication by Schneekloth et al. (ChemBioChem 2005, 6, 40-46) titled “Chemical Approaches to Controlling Intracellular Protein Degradation” described the state of the field at the time.
The publication by Schneekloth et al. (Bioorg. Med. Chem. Lett. 2008, 18, 5904-5908) titled “Targeted Intracellular Protein Degradation Induced by a Small Molecule: En Route to Chemical Proteomics” describes a degradation agent that consists of two small molecules linked by PEG that in vivo degrades the androgen receptor by concurrently binding the androgen receptor and ubiquitin E3 ligase.
WO 2013/170147 filed by Crews et al. titled “Compounds Useful for Promoting Protein Degradation and Methods of Using Same” describes compounds comprising a protein degradation moiety covalently bound to a linker, wherein the C log P of the compound is equal to or higher than 1.5. In particular, the specification discloses protein degrading compounds that incorporate certain small molecules that can bind to an E3 ubiquitin ligase.
In unrelated parallel research, scientists were investigating thalidomide toxicity. Ito et al. (Science 2010, 327, 1345-1350) titled “Identification of a Primary Target of Thalidomide Teratogenicity”, described that cereblon is a thalidomide binding protein. Cereblon forms part of an E3 ubiquitin ligase protein complex which interacts with damaged DNA binding protein 1, forming an E3 ubiquitin ligase complex with Cullin 4 and the E2-binding protein ROC1 (also known as RBX1) where it functions as a substrate receptor to select proteins for ubiquitination. The study revealed that thalidomide-cereblon binding in vivo may be responsible for thalidomide teratogenicity. After the discovery that thalidomide causes teratogenicity in the mid-1960's, the compound and related structures were notwithstanding found to be useful as anti-inflammatory, anti-angiogenic and anti-cancer agents (see Bartlett et al. (Nat. Rev. Cancer 2004, 4, 314-322) titled “The Evolution of Thalidomide and Its Imid Derivatives as Anticancer Agents”).
The disclosure that thalidomide binds to the cereblon E3 ubiquitin ligase led to research to investigate incorporating thalidomide and certain derivatives into compounds for the targeted destruction of proteins. Two seminal papers were published in Science in 2014: G. Lu et al., The Myeloma Drug Lenalidomide Promotes the Cereblon-Dependent Destruction of Ikaros Proteins, Science, 343, 305-309 (2014); and J. Kronke et al., Lenalidomide Causes Selective Degradation of IKZF1 and IKZF3 in Multiple Myeloma Cells, Science, 343, 301-305 (2014).
U.S. 2014/0356322 assigned to Yale University, GlaxoSmithKline, and Cambridge Enterprise Limited University of Cambridge titled “Compounds and Methods for the Enhanced Degradation of Target Proteins & Other Polypeptides by an E3 Ubiquitin Ligase” describes protein degrading compounds that bind to the VHL E3 Ubiquitin Ligase. See also Buckley et al. (J. Am. Chem. Soc. 2012, 134, 4465-4468) titled “Targeting the Von Hippel-Lindau E3 Ubiquitin Ligase Using Small Molecules to Disrupt the Vhl/Hif-1alpha Interaction”.
Additional publications in this area include the following: Lu et al. (Chem. Biol. 2015, 22, 755-763) titled “Hijacking the E3 Ubiquitin Ligase Cereblon to Efficiently Target Brd4”; Bondeson et al. (Nat. Chem. Biol. 2015, 11, 611-617) titled “Catalytic in Vivo Protein Knockdown by Small-Molecule Protacs”; Gustafson et al. (Angewandite Chemie, International Edition in English 2015, 54, 9659-9662) titled “Small-Molecule-Mediated Degradation of the Androgen Receptor through Hydrophobic Tagging”; Lai et al. (Angewamdte Chemie, International Edition in English 2016, 55, 807-810) titled “Modular Protac Design for the Degradation of Oncogenic Bcr-Abl”; Toure et al. (Angew. Chem. Int. Ed. 2016, 55, 1966-1973) titled “Small-Molecule Protacs: New Approaches to Protein Degradation”; and Winter et al. (Science 2015, 348, 1376-1381) titled “Drug Development. Phthalimide Conjugation as a Strategy for in Vivo Target Protein Degradation” describes thalidomide based Target Protein degradation technology.
WO 2015/160845 assigned to Arvinas Inc. titled “Imide Based Modulators of Proteolysis and Associated Methods of Use” describes protein degradation compounds that incorporate thalidomide and certain derivatives which bind to a cereblon E3 ligase. Additional patent applications filed by Arvinas Inc. directed towards the degradation of a Target Protein using known E3 ligase ligands to direct the Target Protein to the proteasome for degradation include U.S. 2016/0058872 titled “Imide Based Modulators of Proteolysis and Associated Methods of Use”; U.S. 2016/0045607 titled “Estrogen-related Receptor Alpha Based PROTAC Compounds and Associated Methods of Use”; U.S. 2016/0214972 titled “Compounds and Methods for the Targeted Degradation of Androgen Receptor”; U.S. 2016/0272639 titled “Compounds and Methods for the Enhanced Degradation of Target Proteins”; U.S. 2017/0008904 titled “MDM2-Based Modulators of Proteolysis and Associated Methods of Use”; U.S. 2017/0037004 titled “Alanine-Based Modulators of Proteolysis and Associated Methods of Use”, U.S. 2017/0065719 titled “Compounds and Methods for the Targeted Degradation of Bromodomain containing proteins”; WO 2016/036036 titled “Tank Binding Kinase-1 PROTACS and Associated Methods of Use”; and WO 2016/197032 “Imide-Based Modulators and Proteolysis and Associated Methods of Use”.
Dana-Farber Cancer Institute has also filed several patent applications directed towards the degradation of a Target Protein using known E3 ligase ligands to direct the Target Protein to the proteasome for degradation. These filings include US 2016/0176916 titled “Methods to Induce Target Protein Degradation through Bifunctional Molecules; WO 2017/024318 titled “Target Protein Degradation to Attenuate Adoptive T-Cell Therapy Associated Adverse Inflammatory Responses”; WO 2017/024317 titled “Methods to Induce Target Protein Degradation through Bifunctional Molecules”; WO 2017/024319 titled “Tunable Endogenous Protein Degradation”; WO 2017/117474 titled “Bifunctional Compounds for HER3 Degradation and Methods of Use”; and WO 2017/117473 titled “Bifunctional Molecules for HER3 Degradation and Methods of Use”.
There is a need for the development of new strategies for targeted protein degradation in a selective manner.